The present invention relates to an electric parking brake mechanism capable of being integrated to an electric brake, particularly relates to an electric parking brake mechanism using an electric motor in an electric brake as a drive source and dispensing with an exclusive actuator.
Conventionally, there have been known various types of electric brakes adopting a mechanism of converting rotational torque of an electric motor into braking force (force transmission converting mechanism) adopting, for example, a ball screw, a roller screw, e ball ramp and the like. In order to enable to use the electric brakes also as parking brakes, a braking force holding mechanism holding braking force (hereinafter, referred to as parking brake mechanism) is needed. There are brake apparatus having such a parking brake mechanism, as described in JP-A-04-108058 (Japanese Patent Application Publication Number: Hei04-108058) and JP-T-2000-514540 (Japanese Patent Application Publication Number: 2000-514540).
An electric brake described in JP-A-108058 is provided with an irreversible mechanism (worm gear) between an electric actuator and a brake mechanism for permitting power transmission only from the electric actuator to the brake mechanism, and is provided with a vehicle state detector for determining a stationary state and a running state of a vehicle, and used as a parking brake by controlling electricity conduction to the electric motor based on an output signal of the vehicle state detector.
Further, a disc brake of an electric type described in JP-T-2000-514540 is a disc brake operated electromechanically for an automobile having a brake caliper, an operating apparatus provided at the brake caliper and two of friction linings provided at the brake calipers to be able to carry out restricted movement by being operated integrally with respective one sides of the brake disc, one of the friction linings is directly engaged with the brake disc via the operating apparatus by an operating member, other of the friction linings is engaged with the brake disc by way of an effect of reaction force by the brake caliper, further, the operating apparatus is provided with an electric motor provided coaxially with the operating member similar to a reduction gear provided between the electric motor and the operating member, and when current supplied to the electric motor is cut after the electric motor has been activated, parking brake operation of constitute by hampering reverse rotation of a rotor of the electric motor by an electromagnet.
However, according to the constitution described in JP-A-04-108058, a reduction gear of a worm gear type is used as the irreversible mechanism and therefore, mechanical efficiency is poor, the electric motor needs to be large-sized in order to sufficiently increase pressing force and it is difficult to downsize a total of the apparatus.
Further, according to a constitution described in JP-T-2000-514540, the actuator (electromagnet) exclusive for the parking brake is needed for operating the parking brake and there poses a problem that a number of parts is increased and downsizing of the apparatus is difficult and so on.